This invention comprises a method of preparing a melt for mineral fibre production comprising introducing a mixture of mineral fibre forming raw material into a shaft furnace and heating the mixture by means of a plasma gas stream formed in a plasma torch, discharging the melt thus formed from the bottom of the shaft furnace and passing the melt to a fiberizing apparatus in which the melt is converted into mineral fibres.
International patent publication No. W087/06926 discloses a method of the above-mentioned type.
Various by-products which are generally called mineral wool waste are formed during the manufacture of mineral wool. These by-products include a fine power-like material which is formed in connection with the cutting, e.g. edge cutting, of mineral wool mats so as to form mineral wool slabs having desired dimensions. The term mineral wool waste also includes pieces of such mineral wool slabs which pieces may contain the binder used during the production of the mineral wool slabs in a cured or non-cured state.
The waste material obtained by conventional mineral fibre production thus exists in varying form viz. ranging from a fine powder-like material over fibre lumps and pieces of slabs to a coarse slaggy material.
Up to now it has been attempted to get rid of such waste material by dumping it at specially suitable dumping sites in nature. However, it has become increasingly costly and difficult to dispose of the waste material in this manner due to the difficulties in finding suitable dumping sites and the increasing public disapproval against dumping industrial waste products in nature.
Since the waste material has a composition which is essentially the desired one for mineral fibre production but does not have the desired physical shape, it represents an attractive material if it can be recycled to and re-used in mineral fibre production.
The direct introduction of the waste material into the shaft furnace is normally out of the question since it ordinarily is present in the above-mentioned varying physical shapes. Therefore, the waste material cannot be handled by means of the equipment normally used in connection with mineral fibre production. Furthermore, due to its physical state which makes it insulating and prevents air penetration, it adversely affects the melting process in a shaft furnace, in particular when the melting operation is based on combustion of fossil fuels. It has been attempted to re-use waste material from mineral fibre production by converting it into briquettes and to introduce such briquettes into the shaft furnace together with the conventional starting materials. However, such re-use requires admixture of a binder and shaping of the briquettes by pressing or moulding. Apart from significantly increasing the cost of the mineral fibre production, it is difficult to find binders which on one hand impart to the briquettes the required strength and on the other hand are decomposed without creating environmental problems during the melting operation.
International patent publication No. W082/00460 discloses a method of preparing a melt for mineral fibre production. The prior art method comprises the use of a shaft furnace which at its lower end is connected with a melting chamber which is heated by plasma gas formed in a plasma torch located in the melting chamber. Furthermore, there are provided conduits for blowing fine starting materials and mineral fibre waste into the melting chamber.
A prerequisite for introducing waste material from mineral fibre production into the plasma gas in a method of the above-mentioned type is that only fine particles are used or that the waste material is subjected to disintegration in order to have all portions thereof converted into particles. However, such measures require substantial investments and present problems with respect to the handling of the finely divided material.
The object of the invention is to utilize waste material from mineral fibre production and having varying physical shapes in a method of the above-mentioned type without the need of subjecting the waste material to a preceding complete disintegration.